The mod makes significant improvements to the Dark Brotherhood companion summoning spell. Now he is much more useful in battle, less talkative (and therefore less annoying), and can also summon himself. Those summoned will include characters from Oblivion, as well as fallen assassins from the game itself. In addition, you can buy spells that summon the Shadow of Sithis (a dark skeletal mage) and a random assassin from the Dark Brotherhood.